Techniques for studying serotonin turnover in discrete rat brain nuclei were developed in order to study short term changes in 5HT synthesis elicited by psychotropic drug. These methods involved measurement by high pressure liquid chromatography of changes in serotonin, 5-hydroxytryptophan or 5-hydroxyindoleacetic acid concentrations after pharmacologically blocking their metabolism, synthesis or efflux, respectively. BIBLIOGRAPHIC REFERENCES: Meek, J. L. and Lofstrandh, S.: Tryptophan hydroxylase in discrete brain nuclei: Comparison of activity in vitro and in vivo. Europ. J. Pharmacol. 37: 377-380-1976. Neckers, L.M., Biggio, G., Mola, E. and Meek, J. L.: Modulation of brain tryptophan hydroxylase activity in brain tryptophan content. J. Pharmacol. Exp. Ther 201: 110-116, 1977.